YARA External Variables

Raccine

A Simple Ransomware Protection

Why

We see ransomware delete all shadow copies using vssadmin pretty often. What if we could just intercept that request and kill the invoking process? Let's try to create a simple vaccine.

How it works

We register a debugger for vssadmin.exe (and wmic.exe), which is our compiled raccine.exe. Raccine is a binary, that first collects all PIDs of the parent processes and then tries to kill all parent processes.

Advantages:

The method is rather generic
We don't have to replace a system file (vssadmin.exe or wmic.exe), which could lead to integrity problems and could break our raccination on each patch day
Flexible YARA rule scanning of command line params for malicious activity
The changes are easy to undo
Runs on Windows 7 / Windows 2008 R2 or higher
No running executable or additional service required (agent-less)

Disadvantages / Blind Spots:

The legitimate use of vssadmin.exe delete shadows (or any other blacklisted combination) isn't possible anymore
It even kills the processes that tried to invoke vssadmin.exe delete shadows, which could be a backup process
This won't catch methods in which the malicious process isn't one of the processes in the tree that has invoked vssadmin.exe (e.g. via schtasks)

The Process

Invocation of vssadmin.exe (and wmic.exe) gets intercepted and passed to raccine.exe as debugger (vssadmin.exe delete shadows becomes raccine.exe vssadmin.exe delete shadows)
We then process the command line arguments and look for malicious combinations using Yara rules.
If no malicious combination could be found, we create a new process with the original command line parameters.
If a malicious combination could be found, we collect all PIDs of parent processes and the start killing them (this should be the malware processes as shown in the screenshots above). Raccine shows a command line window with the killed PIDs for 5 seconds, logs it to the Windows Eventlog and then exits itself.

Malicious combinations:

delete and shadows (vssadmin, diskshadow)
resize and shadowstorage (vssadmin)
delete and shadowstorage (vssadmin)
delete and shadowcopy (wmic)
delete and catalog and -quiet (wbadmin)
win32_shadowcopy or element from a list of encoded commands (powershell)
recoveryenabled (bcedit)
ignoreallfailures (bcedit)

^ outdated list: check the corresponding YARA rule

Powershell list of encoded commands: JAB, SQBFAF, SQBuAH, SUVYI, cwBhA, aWV4I, aQBlAHgA and many more

Example

Emotet without Raccine - Link

Emotet with Raccine - Link (ignore the process activity that is related to the Raccine installation)

The infection gets nipped in the bud.

Warning !!!

USE IT AT YOUR OWN RISK!

You won't be able to run commands that use the blacklisted commands on a raccinated machine anymore until you apply the uninstall patch raccine-reg-patch-uninstall.reg. This could break various backup solutions that run that specific command during their work. It will not only block that request but kill all processes in that tree including the backup solution and its invoking process.

If you have a solid security monitoring that logs all process executions, you could check your logs to see if vssadmin.exe delete shadows, vssadmin.exe resize shadowstorage ... or the other blocked command lines are frequently or sporadically used for legitimate purposes in which case you should refrain from using Raccine.

Version History

0.1.0 - Initial version that intercepted & blocked all vssadmin.exe executions
0.2.0 - Version that blocks only vssadmin.exe executions that contain delete and shadows in their command line and otherwise pass all parameters to a new process that invokes vssadmin with its original parameters
0.2.1 - Removed explorer.exe from the whitelist
0.3.0 - Supports the wmic method calling delete shadowcopy, no outputs for whitelisted process starts (avoids problems with wmic output processing)
0.4.0 - Supports logging to the Windows Eventlog for each blocked attempt, looks for more malicious parameter combinations
0.4.1 - Statically linked binaries
0.4.2 - Bugfixes provided by John Lambert
0.5.0 - Removed Eventlog logging (basic info was unnecessary; cuased higher complexity; can be achieved by process creation logging as well), support for wbadmin filtering
0.5.1 - Improvements by @JohnLaTwC
0.5.2 - Additional check for delete shadowstorage by @JohnLaTwC, code review by @_hillu, application icon
0.5.3 - Batch installer
0.6.0 - Additional checks for bcdedit.exe /set {default} bootstatuspolicy ignoreallfailures and bcdedit.exe /set {default} recoveryenabled no
0.7.0 - Additional checks for powershell.exe and win32_shadowcopy or a list of encoded commands
0.7.1 - Improvements by @JohnLaTwC
0.7.2 - Using absolute paths in registry patches
0.8.0 - Creates a log file with all intercepted requests and actions performed C:\ProgramData\Raccine_log.txt
0.9.0 - Logs to Windows Eventlog by @JohnLaTwC
0.10.0 - Simulation mode only
0.10.1 - Fix for Simulation mode
0.10.2 - Includes diskshadow.exe delete shadows command
0.10.3-5 - Minor fixes and additions
1.0 BETA - GUI elements and YARA rule scanning of command line params
1.1 BETA - YARA rule matching with external variables, troubleshooting functions
1.2 BETA - Signature Updater
1.3 BETA - In-Memory YARA Scanning of invoking parent process
1.4 BETA - Full x86 support, moved static strings to YARA rules to avoid AV detections, Log of accepted executions, .NET Framework setup in installer
1.4.2 BETA - Exit code fix (pass through of exit code returned by the intercepted program), intercept taskkill.exe

Installation

Requirements

VC++ Runtime for YARA scanning (Installer contains the setup package from https://aka.ms/vs/16/release/VC_redist.x64.exe)
.NET Framework 4.5
Internet access for the YARA rule updates
Windows 7 / Windows 2008 R2 or higher

Both the Visual C++ Redistributable package and the .NET Framework will be automatically installed running install-raccine.bat.

Automatic Installation

Download Raccine.zip from the Release section
Extract it
Run raccine-installer.bat as administrator

The batch installer includes an "uninstall" option.

Manual Uninstall

As Administrator do:

Run raccine-reg-patch-uninstall.reg
Remove %ProgramFiles%\Raccine and %ProgramData%\Raccine folders
Run reg delete HKCU\Software\Raccine /F
Run taskkill /F /IM RaccineSettings.exe
Run reg delete "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /V "Raccine Tray" /F
Run schtasks /DELETE /TN "Raccine Rules Updater" /F

Updates

Program Upgrade

We recommend an uninstall and reinstall to upgrade. An uninstall removes all registry keys with configurations.

Signature Update

Raccine has an integrated signature-updater since version 1.2. This program named RaccineRulesSync.exe is configured to run once a day via scheduled task. You can run a signature update manually using the option in the tray icon menu.

YARA Matching

Since version 1.0, Raccine additionally uses YARA rules to determine if a process command line or parent process is malicious or not. Raccine uses 2 sets of rules for two different purposes.

./yara - rules that get applied to the command line with all parameters, e.g. WMIC.exe delete justatest
./yara/in-memory - rules that get applied to process memory of the parent process of our intercepted process, e.g. ransomware.exe running our intercepted process vssadmin.exe

Since version 1.1 we pass a list of external variables into the YARA matching process to allow for much more complex and clever YARA rules that take attributes of the process and its parent into account.

Variable	Description	Example Value
FromRaccine		true
Name	Image file name	WMIC.exe
ExecutablePath	Full path to binary	C:\Windows\System32\wbem\WMIC.exe
CommandLine	Full command line with parameters	WMIC.exe delete justatest
Priority	Process priority	32
ParentName	Parent image file name	cmd.exe
ParentExecutablePath	Full path to parent executable	C:\Windows\System32\cmd.exe
ParentCommandLine	Full parent command line with parameters	C:\WINDOWS\system32\cmd.exe
ParentPriority	Parent process priority	32

The matching process looks like this on the command line:

"C:\Program Files\Raccine\yara64.exe" -d FromRaccine="true" -d Name="WMIC.exe" -d ExecutablePath="C:\Windows\System32\wbem\WMIC.exe" -d CommandLine="WMIC.exe delete justatest" -d  Priority=32 -d FromRaccine="true" -d ParentName="cmd.exe" -d ParentExecutablePath="C:\Windows\System32\cmd.exe" -d ParentCommandLine="'C:\WINDOWS\system32\cmd.exe' " -d ParentPriority=32 C:\ProgramData\Raccine\yarayara\mal_emotet.yar C:\ProgramData\Raccine\yara\Rac1C6A.tmp

The following listing shows an example YARA rule that makes use of the external variables in its condition.

rule env_vars_test {
    condition:
        Name contains "WMIC.exe"
        and CommandLine contains "delete justatest"
        and ParentPriority >= 8
        and (
            ParentCommandLine contains "cmd"
            or ParentCommandLine contains "powershell"
        )
}

Deploy Configuration via GPO

The folder GPO includes Raccine.ADMX and Raccine.ADML. In deployment the Raccine.ADMX file goes in C:\Windows\PolicyDefinitions. The accompanying Raccine.ADML files goes in C:\Windows\PolicyDefinitions\en-US.

To use: Open GPEDIT.MSC > Computer Configuration > Administrative Templates > System > Raccine

After configuring the changes, you may need to bump gpo by running gpupdate.exe.

Logfile

A logfile with all interceptions and actions taken is written to C:\ProgramData\Raccine\Raccine_log.txt

Windows Eventlog

An entry is generated by every blocking event in the Application eventlog.

The IDs that Raccine generates

EventId 1 - Setup activity
EventId 2 - Malicious activity detected
EventId 3 - Benign activity detected

Simulation Mode

Since version 0.10.0, Raccine can be installed in "simulation mode", which activates all triggers, logs all actions but doesn't kill anything. This mode should be used in environments in which backup solutions or other legitimate software for a reasonable amount of time to check if Raccine would interfere with other software. The idea is to install Raccine in simulation mode, let it log for a week or month and then check the logs to see if it would have blocked legitimate software used in the organisation.

Screenshot

Run raccine.exe and watch the parent process tree die (screenshot of v0.1)

GUI

Available and required since version 1.

Pivot

In case that the Ransomware that your're currently handling uses a certain process name, e.g. taskdl.exe, you could just change the .reg patch to intercept calls to that name and let Raccine kill all parent processes of the invoking process tree.

Help Wanted

I'd like to extend Raccine but lack the C++ coding skills, especially on the Windows platform.

Help - My System is Broken

If anything happens to your installation, e.g. sudden error messages, broken services or programs that won't start anymore, run the file raccine-reg-patch-uninstall.reg in the reg-patches sub folder. This should bring everything back to normal.

After that your should also be able to run a full uninstallation using install-raccine.bat.